1. Field of the Invention
The present invention relates to hard disk drive covers for hard disk drive assemblies and methods of manufacturing hard disk drive covers.
2. Description of Related Art
Hard disk drives and related drive assembly components are contained in a disk drive motor base assembly (“base assembly”). A hard disk drive cover (“cover”) made of a metal is mounted on the base assembly. The cover protects the base assembly from externally introduced particles, chemical compounds in the outside environment, or other types of contamination.
FIG. 1 is a top perspective illustration of a cover 13 having an outer surface 15 and a base assembly 11. FIG. 2 is a bottom perspective illustration of the cover 13 having an inner surface 17 and the base assembly 11. FIG. 3 is a top perspective illustration of the cover 13 showing the outer surface 15. FIG. 4 is a bottom perspective illustration of the cover 13 showing the inner surface 17.
The top (outer) surface 15 and bottom (inner) surface 17 are both textured using a common metal surface texturing procedure. The surfaces 15 and 17 of the cover 13 have the same textured surface finish, as shown in FIGS. 1-4. The textured surfaces enhance the visual appearance of the cover 13, preventing and/or hiding scratches and visual blemishes. The textured surface finish has a relatively high roughness average (Ra).
Ra is a measure of an average of vertical deviations of peaks and valleys of a surface. Ra is quantified by measuring vertical deviations of a surface using a profilometer per ASTM standard B46.1. For example, each of the opposing surfaces 15 and 17 of the cover 13 has a textured “2D” surface finish as defined by the ASTM standard A480. A 2D surface finish has a roughness average in the range of 0.4-1.0 micrometers (μm). Ra may be measured, using other metrics. For example, roughness may be measured using root mean square, maximum valley depth/maximum peak height, maximum height of the profile, skewness, kurtosis, average distance between the highest and lowest valley in each sampling segment, and various other metrics.
Electroless nickel (EN) plating is an auto-catalytic chemical process that deposits a layer of nickel-phosphorus or nickel-boron alloy on a metal surface. An EN plated cover enhances cleanliness because it creates a continuous tightly bonded coating. An EN plated cover also reduces scratches due to its hardness rather than its roughness or texture. However, EN plating is very expensive, particularly for the relatively large surface area of the hard disk cover. Most cost-sensitive hard disk drive covers are passivated stainless steel as it is the most cost-effective solution available. However, passivated covers do not meet cleanliness requirements.
Hard disk drive builders require and have been seeking a hard disk drive cover that can meet strict cleanliness requirement in addition to providing a good visual appearance. A problem associated with utilizing the same textured finish on the top surface 15 and the bottom surface 17 of the cover 13 is that the textured bottom surface 17 does not meet cleanliness requirements. Textured surfaces are rough and not easily cleaned. Furthermore, they shed a greater amount of particles. Particles of metal and metal oxide, for example, down to less than or equal to 0.1 μm (micrometers) in size can cause drive reliability issues. This type of cover does not meet the cleanliness requirements of hard disk drive builders and users.
There is an urgent need for a hard disk drive cover that can meet both stringent cleanliness requirements and visual appearance requirements. There is also a need for a cost-effective and reliable method of manufacturing a hard disk drive cover that meets the required cleanliness and visual appearance requirements.